linux-kernel - Re: unaligned accesses in SLAB etc.

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Date:	Tue, 14 Oct 2014 08:52:19 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	mroos@...ux.ee
Cc:	David Miller <davem@...emloft.net>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	sparclinux@...r.kernel.org
Subject: Re: unaligned accesses in SLAB etc.

On Mon, Oct 13, 2014 at 11:22:37PM +0300, mroos@...ux.ee wrote:
> > From: David Miller <davem@...emloft.net>
> > Date: Sat, 11 Oct 2014 22:15:10 -0400 (EDT)
> > 
> > > 
> > > I'm getting tons of the following on sparc64:
> > > 
> > > [603965.383447] Kernel unaligned access at TPC[546b58] free_block+0x98/0x1a0
> > > [603965.396987] Kernel unaligned access at TPC[546b60] free_block+0xa0/0x1a0
> > > [603965.410523] Kernel unaligned access at TPC[546b58] free_block+0x98/0x1a0
> 
> > In all of the cases, the address is 4-byte aligned but not 8-byte
> > aligned.  And they are vmalloc addresses.
> > 
> > Which made me suspect the percpu commit:
> > 
> > ====================
> > commit bf0dea23a9c094ae869a88bb694fbe966671bf6d
> > Author: Joonsoo Kim <iamjoonsoo.kim@....com>
> > Date:   Thu Oct 9 15:26:27 2014 -0700
> > 
> >     mm/slab: use percpu allocator for cpu cache
> > ====================
> > 
> > And indeed, reverting this commit fixes the problem.
> 
> I tested Joonsoo Kim's fix and it gets rid of the kernel unaligned 
> access messages, yes.
> 
> But the instability on UltraSparc II era machines still remains - 
> occassional Bus Errors during kernel compilation, messages like this:
> 
> sh[11771]: segfault at ffd6a4d1 ip 00000000f7cc5714 (rpc 00000000f7cc562c) sp 00000000ffd69d90 error 30002 in libc-2.19.so[f7c44000+16a000]

Hello, Meelis.

Thanks for testing.

I'd like to know that your another problem is related to commit
bf0dea23a9c0 ("mm/slab: use percpu allocator for cpu cache").
So, if the commit is reverted, your another problem is also gone completely?

Thanks.
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